Printing plates using binder resins having polyethylene oxide segments

ABSTRACT

The present invention relates to a polymerizable coating composition suitable for the manufacture of printing plates, which may be developable on-press. The coating composition comprises (i) a polymerizable compound and (ii) a polymeric binder comprising polyethylene oxide segments, wherein the polymeric binder is selected from the group consisting of at least one graft copolymer comprising a main chain polymer and polyethylene oxide side chains, a block copolymer having at least one polyethylene oxide block and at least one non-polyethylene oxide block, and a combination thereof. The invention is also directed to an imageable element comprising a substrate and the polymerizable coating composition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/119,454 filed Apr. 10, 2002, now U.S. Pat. No. 6,899,994 that is acontinuation-in-part of U.S. patent application Ser. No. 09/826,300filed Apr. 4, 2001, now U.S. Pat. No. 6,582,882. Each of the foregoingapplications is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to negative-working printing plates whichcan be exposed by UV, visible, or infrared radiation. In particular, thepresent invention relates to printing plates comprising polymericbinders containing polyethylene oxide segments.

2. Background of the Invention

Radiation-sensitive compositions are routinely used in the preparationof high-performance printing plate precursors. There are primarily twoways of improving the properties of radiation-sensitive compositions andthus also of the corresponding printing plate precursors. The first wayaddresses improvement of the properties of the radiation-sensitivecomponents in the compositions (frequently negative diazo resins orphotoinitiators). The other way deals with improvement of physicalproperties of the radiation-sensitive layers through the use of novelpolymeric compounds (“binders”).

The latest developments in the field of printing plate precursors dealwith radiation-sensitive compositions which can be imagewise exposed bymeans of lasers or laser diodes. This type of exposure does not requirefilms as intermediate information carriers since lasers can becontrolled by computers.

High-performance lasers or laser diodes which are used in commerciallyavailable image-setters emit light in the wave-length ranges of between800 to 850 nm and between 1060 and 1120 nm, respectively. Therefore,printing plate precursors, or initiator systems contained therein, whichare to be imagewise exposed by means of such image-setters have to besensitive in the near IR range. Such printing plate precursors can thenbasically be handled under daylight conditions which significantlyfacilitates their production and processing.

There are two possible ways of using radiation-sensitive compositionsfor the preparation of printing plates. For negative printing plates,radiation-sensitive compositions are used wherein after an imagewiseexposure the exposed areas are cured. In the developing step, only theunexposed areas are removed from the substrate. For positive printingplates, radiation-sensitive compositions are used whose exposed areasdissolve faster in a given developing agent than the non-exposed areas.This process is referred to as photo-solubilization.

Negative-working plates typically require after imagewise exposure apreheating step, as described for example in EP 0 672 544, EP 0 672 954as well as U.S. Pat. No. 5,491,046 and EP 0 819 985. These platesrequire a preheating step within a very narrow temperature range whichonly causes a partial crosslinking of the image layer. To meet currentstandards regarding the number of printable copies and the resistance topress room chemicals, an additional heating step—referred to as a postbake step—is carried out during which the image layer is crosslinkedfurther.

U.S. Pat. No. 4,997,745 describes photosensitive compositions comprisinga dye absorbing between 300 and 900 nm and a trihalomethyl-s-triazinecompound.

In U.S. Pat. No. 5,496,903 and DE 196 48 313, photosensitivecompositions are described which in addition to a dye absorbing in theIR range comprise borate co-initiators; also, halogenated s-triazinesare described as further co-initiators.

Further photopolymerizable compositions with initiator systems aredescribed in U.S. Pat. No. 5,756,258, U.S. Pat. No. 5,545,676, U.S. Pat.No. 5,914,215, JP 11-038633, JP 09-034110, U.S. Pat. No. 5,763,134 andEP 0 522 175.

U.S. Pat. No. 6,245,486 discloses radiation sensitive printing plates,including on-press developable plates. However, this patent requirescompositions having an IR ablatable mask layer over a UV addressable,negative-working, on press developable, free radical polymerizablelayer.

U.S. Pat. No. 6,245,481 discloses IR-ablatable, UV-photopolymerizabletwo-layer compositions that require IR exposure followed by UV floodirradiation.

U.S. Pat. No. 5,599,650 discloses UV addressable, negative-working, onpress developable printing plates based on free radical polymerization.This patent requires a free radical quencher polymer, specifically onecontaining nitroxide groups, in an overcoat layer to facilitatedevelopability.

U.S. Pat. No. 6,071,675 discloses similar printing plates to U.S. Pat.No. 5,599,650 but additionally requires adding dispersed solid particlesto the imaging layer to improve on-press developability or to reducetackiness.

U.S. Pat. No. 6,309,792 and WO 00/48836 describe IR-sensitivecompositions comprising a polymeric binder, a free radicallypolymerizable system, and a specific initiator system. The compositionsof WO 00/48836 require a preheat step after the exposure for sufficienthardening of the compositions. The printing plate precursors must bedeveloped with an aqueous developer.

U.S. Pat. No. 6,864,040 describes IR sensitive compositions containingleuco dyes additional to those described in U.S. Pat. No. 6,309,792 andWO 00/48836. U.S. Pat. No. 6,864,040 requires a preheat step after IRexposure and an aqueous development step for processing.

U.S. Pat. No. 5,204,222 teaches a composition comprising polymerizableingredients in conjunction with a polymer binder comprising apolyurethane main chain. The side chains of the polymer binder do notcomprise a polyethylene oxide chain.

U.S. Pat. No. 5,800,965 teaches a composition, suitable for flexographicplates, comprising monomers of polyethylene glycol as polymerizablecomponents.

U.S. Pat. No. 6,037,102, also directed to flexographic plates, teaches aphotopolymerizable composition comprising a graft copolymer havingpolyvinyl alcohol grafts on a polyethylene oxide (PEO) main chainpolymer.

EP 1 117 005 discloses photopolymerizable compounds which containpolyethylene oxide chains having 1-10 ethylene oxide units. Theinvention is exemplified by the use of polymers having one ethyleneoxide unit. With more than ten ethylene oxide units, both resolution andwater resistance of cured products decrease. Binder resins havingsufficiently long PEO segments in accordance with the present inventionare not disclosed.

U.S. Pat. No. 6,582,882 discloses graft copolymers comprisingpolyethylene oxide side chains, but does not teach a compositioncomprising polymerizable components or initiators. The side chains mayfurther comprise a hydrophobic segment between the polyethylene oxidesegment and the main chain, and a hydrophobic segment at the terminus ofthe polyethylene oxide side chains.

U.S. Pat. No. 6,846,614 discloses polyalkylene ether polymers andcopolymers, including block copolymers of polyethylene oxide andpolypropylene oxide. However, the polyalkylene ether polymers andcopolymers disclosed in this patent do not provide sufficientdifferentiation for developability of the unexposed areas and durabilityof the exposed image areas.

None of the above patents or patent applications disclose polymerizablecompositions which contain binder resins having PEO segments inaccordance with the present invention.

The present invention therefore satisfies the need in the art for aprinting plate and process for preparing a printing plate that does notrequire a preheat step or a development step. As a result of substantialstudies, it was found that polymerizable compositions, which containcertain polymeric binders having polyethylene oxide (PEO) segments, arereadily developable in aqueous developers, including on-pressdevelopability with fountain solution and printing ink. Furthermore,following imagewise exposure to electromagnetic radiation in theultraviolet, visible or infrared spectral regions, the exposed regionsresist developability and serve as durable, ink receptive image areas,without the need for a predevelopment heating step. Thus, it was foundthat certain polymeric binders having PEO segments, surprisingly,enhance differentiation of the exposed and unexposed areas byfacilitating developability of the unexposed areas together withenhancing durability of the exposed image areas.

SUMMARY OF THE INVENTION

It is therefore one object of the present invention to provide apolymerizable composition comprising a polymerizable compound and apolymeric binder comprising polyethylene oxide segments.

Another object of the present invention is to provide an imageableelement comprising: (a) a substrate; and (b) a polymerizable compositioncoated onto the substrate, the composition comprising (1) apolymerizable compound and (ii) a polymeric binder comprisingpolyethylene oxide segments, wherein the polymeric binder is selectedfrom the group consisting of at least one graft copolymer comprising amain chain polymer and polyethylene oxide side chains, a block copolymerhaving at least one polyethylene oxide block and at least onenon-polyethylene oxide block, and a combination thereof. Preferably, theimageable element may be exposed by one of ultraviolet, visible, andinfrared radiation.

It is still another object of this invention to provide a method forpreparing an on-press developable negative-working printing plate, themethod comprising (a) providing a substrate; (b) applying anegative-working layer comprising a composition onto the substrate,wherein the composition comprises a polymerizable compound and apolymeric binder comprising polyethylene oxide segments; (c) imagingwith one of ultraviolet, visible, and infrared radiation; and (d)developing on a press, wherein the method does not comprise a separatedevelopment step.

This invention allows the manufacture of on-press developable orwater-developable lithographic printing plates imageable by UV exposureframes, infrared laser plate setters, or visible computer-to-plate platesetters. This invention also provides laser addressable, digitallyimaged printing plate precursors, which are developable on press,thereby avoiding a separate development step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows scanning an electron microscope (‘SEM’) image of thecoating of Example 7 discussed herein.

FIG. 2 shows scanning an electron microscope (‘SEM’) image of thecoating of Example 9 discussed herein.

FIG. 3 shows scanning an electron microscope (‘SEM’) image of thecoating of Example 12 discussed herein.

FIG. 4 shows scanning an electron microscope (‘SEM’) image of thecoating of Example 18 discussed herein.

FIG. 5 shows scanning an electron microscope (‘SEM’) image of thecoating of Example 19 discussed herein.

DETAILED DESCRIPTION OF THE INVENTION

The polymerizable compound present in the composition of the inventionpreferably contains a polymerizable group selected from an additionpolymerizable ethylenically unsaturated group, a crosslinkableethylenically unsaturated group, a ring-opening polymerizable group, anazido group, an aryldiazonium salt group, an aryldiazosulfonate group ora combination thereof.

The addition polymerizable ethylenically unsaturated group may bepolymerizable by free radical polymerization, cationic polymerization,or a combination thereof. The free radical addition polymerizableethylenically unsaturated group is preferably selected from the groupconsisting of a methacrylate group, an acrylate group, and a combinationthereof. The cationic addition polymerizable ethylenically unsaturatedgroup is preferably selected from the group consisting of a vinyl ether,a vinyl aromatic compound, including styrene and alkoxy styrenederivatives, and a combination thereof.

The crosslinkable ethylenically unsaturated group is preferably selectedfrom the group consisting of a dimethylmaleimide group, a chalconegroup, and a cinnamate group.

The ring-opening polymerizable group is preferably selected from thegroup consisting of an epoxide, an oxetane, and a combination thereof.

The polymerizable compound of the invention is present in sufficientamount to render the composition insoluble in an aqueous developer afterexposure to radiation. The weight ratio of polymerizable compound topolymeric binder ranges from about 5:95 to about 95:5, preferably fromabout 10:90 to about 90:10, more preferably from about 20:80 to about80:20, most preferably from about 30:70 to about 70:30.

The polymerizable composition preferably comprises a free radicaladdition polymerizable composition, including polymerizableethylenically unsaturated compounds and a photoinitiator system forgenerating initiating free radicals. The polymerizable composition mayfurther contain a copolymerizable compound comprising at least two thiolgroups. Photo initiating systems, which are, active to electromagneticradiation in the ultraviolet, visible and/or infrared spectral regions,may be used, corresponding to the spectral range of about 300-1400 nm.Such photoinitiator systems include trichloromethyl triazines alone ortogether with a photosensitizer, for example, as described in U.S. Pat.No. 4,997,745; diaryliodonium salts and a photosensitizer, as describedin U.S. Pat. No. 5,546,258; spectral sensitizers for visible lightactivation, together with trichloromethyltriazines, as described, forexample in U.S. Pat. No. 5,599,650; 3-ketocoumarins, for ultraviolet andvisible light activation, together with a polycarboxylic acidcoinitiator, such as anilino-N,N-diacetic acid, and a secondarycoinitiator, such as diaryliodonium salts, titanocenes, haloalkyltriazines, hexaaryl bisimidizoles, borate salts and photooxidantscontaining a heterocyclic nitrogen atom that is substituted by an alkoxyor acyloxy group, as described in U.S. Pat. No. 5,942,372; a cyaninedye, diaryliodonium salt and a coinitiator having a carboxylic acidgroup bonded via a methylene group to a N, O or S group, which isdirectly attached to an aromatic ring, as described in U.S. Pat. No.5,368,990; a cyanine dye, for infrared radiation activation, togetherwith a trichloromethyltriazine and an organoboron salt, as described inU.S. Pat. No. 5,496,903; an infrared radiation absorber, a compoundcapable of producing an initiating free radical, includingtrichloromethyl triazines and azinium compounds and a polycarboxylicacid coinitiator having a carboxylic acid group bonded via a methylenegroup to a N, O S group, which is directly attached to an aromatic ring,as described in U.S. Pat. No. 6,309,792.

Preferred photoinitiator systems include an ultraviolet, visible orinfrared absorber, an electron acceptor capable of producing initiatingfree radicals, and a coinitiator capable of donating an electron and/orhydrogen atom and/or of forming an initiating free radical. The amountof radiation absorber is the amount required to render the compositioninsoluble to an aqueous developer after exposure to radiation.Preferably, the concentration of the radiation absorber is in the rangeto provide a molar absorptivity in the range of about 0.05 to 3 mol 1⁻¹cm⁻¹, preferably about 0.1 to 1.5 mol 1⁻¹ cm⁻¹, more preferably 0.3 to1.0 mol 1⁻¹ cm⁻¹.

Preferred IR absorbers for photo/thermal activation are squarylium dyes,croconate dyes, triarylamine dyes, thiazolium dyes, indolium dyes,oxazolium dyes, cyanine and merocyanine dyes, polyaniline dyes,polypyrrole dyes, polythiophene dyes, chalcogenopyryloarylidene andbis(chalcogenopyrylo)polymethine dyes, oxyindolizine dyes, pyrylium dyesand phthalocyanine pigments. Other useful classes include azulenium andxanthene dyes, as well as carbon blacks, metal carbides, borides,nitrides, carbonitrides and bronze-structured oxides. Cyanine dyes areparticularly preferred.

In another embodiment, the polymerizable composition preferablycomprises a condensate of an aryldiazonium salt or mixture ofaryldiazonium salts with a condensable compound. The condensablecompound is preferably selected from the group consisting of aldehydes,bis-methoxymethyl diphenyl ether, and mixtures thereof. Thepolymerizable composition comprising the condensate of an aryldiazoniumsalt preferably also comprises a co-reactive binder.

The aryldiazonium condensate polymerizable compositions may furthercontain a free-radical addition polymerizable composition, includingpolymerizable ethylenically unsaturated compounds and a photoinitiatorsystem for generating initiating free radicals, as described above. Suchcompositions are known as diazo photopolymer hybrid compositions.

The polymerizable composition of the invention comprises a polymerizablecompound and a polymeric binder comprising polyethylene oxide segments,wherein the polymeric binder is selected from graft copolymers having amain chain polymer and polyethylene oxide (PEO) side chains or blockcopolymers having PEO together with non-PEO blocks.

Preferably the graft and block copolymers are amphiphilic, whichsignifies that they comprise both hydrophilic and hydrophobic segments.Such amphiphilic copolymers also tend to be surface active. The PEOsegments are hydrophilic. Although not bound by any theory, thecombination of hydrophobic and hydrophilic segments is considered to beimportant for enhancing differentiation of the exposed and unexposedareas.

The glass transition temperature T_(g) of the polymeric binder used inthis invention preferably ranges from about 35 to about 220° C., morepreferably from about 45 to about 140° C., most preferably from about 50to about 130° C. The polymeric binder having T_(g) values in the rangespecified above is a solid and is preferably non-elastomeric. Thepolymeric binders may be crosslinked, but are preferably uncrosslinked.The glass transition temperature T_(g) of the main chain polymer of thegraft copolymer and the non-PEO block of the block copolymer preferablyranges from 40 to about 220° C., more preferably from about 50 to about140° C., most preferably from about 60 to about 130° C.

Preferably, the graft and block copolymers have number average molecularweights from about 2,000 to about 2,000,000. Preferably the numberaverage molecular weight (Mn) of the PEO segments ranges from about 500to about 10,000, more preferably from about 600 to about 8,000, mostpreferably from about 750 to about 4,000. When the Mn values are lessthan about 500, there is insufficient hydrophilic segment to adequatelypromote aqueous developability. However, ink receptivity of the imageareas tends to decrease with increasing Mn values of the polyethyleneoxide segments, which approach 10,000.

The amount of PEO segments in the graft copolymers ranges from about 0.5to about 60% by weight, preferably about 2 to about 50% by weight, morepreferably about 5 to about 40% by weight, most preferably about 5 toabout 20% by weight. The amount of PEO segments in the block copolymersranges from about 5 to about 60% by weight, preferably about 10 to about50% by weight, more preferably about 10 to about 30% by weight. At thelow levels of PEO segments in the graft and block copolymers,developability tends to decrease, whereas at the high levels, inkreceptivity of the image areas tends to decrease.

The polymeric binder is present in sufficient amount to render thephotopolymerizable composition soluble or dispersible in an aqueousdeveloper. Preferably, the amount of polymeric binder ranges from about10% to 90% by weight of the composition, more preferably from about 30%to 70% by weight. Aqueous developability tends to increase withincreasing level of PEO segments in the polymeric binder. However, atexcessively high PEO levels, ink receptivity of the image areas tends todecrease.

Preferably, the graft copolymer has a hydrophobic polymer backbone and aplurality of pendant groups represented by:-Q-W—Ywherein Q is a difunctional connecting group; W is selected from thegroup consisting of a hydrophilic segment and a hydrophobic segment; Yis selected from the group consisting of a hydrophilic segment and ahydrophobic segment; with the proviso that when W is a hydrophilicsegment, Y is selected from the group consisting of a hydrophilicsegment and a hydrophobic segment; with the further proviso that when Wis hydrophobic, Y is a hydrophilic segment.

The term “graft” polymer or copolymer in the context of the presentinvention refers to a polymer which has as a side chain a group having amolecular weight of at least 200. Such graft copolymers can be obtained,for example, by anionic, cationic, non-ionic, or free radical graftingmethods, or they can be obtained by polymerizing or co-polymerizingmonomers, which contain such groups. The term “polymer” in the contextof the present invention refers to high and low molecular weightpolymers, including oligomers, and includes homopolymers and copolymers.The term “copolymer” refers to polymers that are derived from two ormore different monomers. The term “backbone” in the context of thepresent invention refers to the chain of atoms in a polymer to which aplurality of pendant groups are attached. An example of such a backboneis an “all carbon” backbone obtained from the polymerization of anolefinically unsaturated monomer.

The graft copolymer preferably comprises repeating units where each unitis represented by the formula

wherein each of R¹ and R² is independently selected from the groupconsisting of: —H, alkyl, aryl, aralkyl, alkaryl, halogen and cyano;

-   Q is selected from the group consisting of:

wherein R³ is selected from the group consisting of: —H and alkyl; R⁴ isselected from the group consisting of: —H, alkyl, halogen, cyano, nitro,alkoxy, alkoxycarbonyl, acyl and a combination thereof,

-   W is selected from the group consisting of: a hydrophilic segment    and a hydrophobic segment;-   Y is selected from the group consisting of: a hydrophilic segment    and a hydrophobic segment;-   Z is selected from the group consisting of: —H, alkyl, halogen,    cyano, acyloxy, alkoxy, alkoxycarbonyl, hydroxyalkyloxycarbonyl,    acyl, aminocarbonyl, aryl and substituted aryl;-   with the proviso that when W is a hydrophilic segment, Y is selected    from the group consisting of a hydrophilic segment and a hydrophobic    segment, with the further proviso that when W is hydrophobic, Y is a    hydrophilic segment.

In one embodiment, the graft copolymer of the present inventioncomprises main chain segments that are predominately hydrophobic andbranch segments that are predominately hydrophilic.

In a second embodiment, the graft copolymer comprises main chainsegments that are predominately hydrophobic and branch segmentscomprising both hydrophobic and hydrophilic segments.

The hydrophilic segment in W in the graft copolymer of the presentinvention is preferably a segment represented by:

wherein each of R⁷, R⁸, R⁹ and R¹⁰ is hydrogen; R³ can be —H or alkyl;and n is from about 12 to about 250. The hydrophobic segment in W can be—R¹²—, —O—R¹²—O—, —R³N—R¹²—NR³—, —OOC—R¹²—O— or —COO—R¹²—O—, whereineach R¹² can independently be a linear, branched or cyclic alkylene of6-120 carbon atoms, a haloalkylene of 6-120 carbon atoms, an arylene of6-120 carbon atoms, an alkarylene of 6-120 carbon atoms or an aralkyleneof 6-120 carbon atoms; and R³ can be —H or alkyl.

The hydrophilic segment in Y can be —H, —R¹⁵, —OH, —OR¹⁶, —COOH,—COOR¹⁶, —O₂CR¹⁶, a segment represented by:

wherein each of R⁷, R⁸, R⁹ and R¹⁰ is hydrogen; R³ can be —H or alkyl;wherein each R¹³, R¹⁴, R¹⁵ and R¹⁶ can independently be —H or alkyl of1-5 carbon atoms and n is from about 12 to about 250. The hydrophobicsegment in Y can be a linear, branched or cyclic alkyl of 6-120carbonatoms, a haloalkyl of 6-120 carbon atoms, an aryl of 6-120 carbon atoms,an alkaryl of 6-120 carbon atoms, an aralkyl of 6-120 carbon atoms,—OR¹⁷, —COOR¹⁷ or —O₂CR¹⁷, wherein R¹⁷ is an alkyl of 6-20 carbon atoms.

In a preferred embodiment, the graft copolymer comprises repeating unitsrepresented by:

wherein each of R¹ and R² can independently be —H, alkyl, aryl, aralkyl,alkaryl, halogen or cyano;

-   wherein Q can be one of:

and wherein R³ can be —H or alkyl; R⁴ can independently be —H, alkyl,halogen, cyano, nitro, alkoxy, alkoxycarbonyl, acyl or a combinationthereof,

-   W is selected from the group consisting of: a hydrophilic segment    and a hydrophobic segment;-   Y is selected from the group consisting of: a hydrophilic segment    and a hydrophobic segment;-   Z is selected from the group consisting of —H, alkyl, halogen,    cyano, acyloxy, alkoxy, alkoxycarbonyl, hydroxyalkyloxycarbonyl,    acyl, aminocarbonyl, aryl and substituted aryl, where the    substituent in the above substituted aryl can be alkyl, halogen,    cyano, alkoxy or alkoxycarbonyl, and the alkyl group is preferably    an alkyl of 1 to 22 carbon atoms;-   with the proviso that when W is a hydrophilic segment, Y is selected    from the group consisting of a hydrophilic segment and a hydrophobic    segment, with the further proviso that when W is hydrophobic, Y is a    hydrophilic segment.

The segment W can be a hydrophilic segment or a hydrophobic segment,wherein the hydrophilic segment can be a segment represented by:

wherein each of R⁷, R⁸, R⁹ and R¹⁰ is hydrogen; R³ can be —H or alkyland n is from about 12 to about 250. The hydrophobic segment can be—R¹²—, —O—R¹²—O—, —R³N—R¹²—NR³—, OOC—R¹²—O—, or —COO—R¹²—O—, whereineach R¹² can independently be a linear, branched or cyclic alkylene of6-120 carbon atoms, a haloalkylene of 6-120 carbon atoms, an arylene of6-120 carbon atoms, an alkarylene of 6-120 carbon atoms or an aralkyleneof 6-120carbon atoms; R³ can be —H or alkyl.

Y can be a hydrophilic segment or a hydrophobic segment, wherein thehydrophilic segment can be —H, —R¹⁵, —OH, —OR¹⁶, —COOH, —COOR¹⁶,—O₂CR¹⁶, a segment represented by:

wherein each of R⁷, R⁸, R⁹ and R¹⁰ is hydrogen; R³ can be —H or alkyl;wherein each R¹³, R¹⁴, R¹⁵ and R¹⁶ can be —H or alkyl of 1-5 carbonatoms and n is from about 12 to about 250. The hydrophobic segment in Ycan be a linear, branched or cyclic alkyl of 6-120 carbon atoms, ahaloalkyl of 6-120 carbon atoms, an aryl of 6-120 carbon atoms, analkaryl of 6-120 carbon atoms, an aralkyl of 6-120 carbon atoms, —OR¹⁷,—COOR¹⁷ or —O₂CR¹⁷, wherein R¹⁷ can be an alkyl of 6-20 carbon atoms.

In another preferred embodiment, the segment W—Y can be represented by:—(OCH₂CH₂)_(n)—OCH₃wherein n is from about 12 to about 75. In this preferred embodiment,the graft copolymer has, for example, repeating units represented by:

wherein n is from about 12 to about 75. More preferably, n has anaverage value of about 45.

In another preferred embodiment, the graft copolymer comprises repeatingunits represented by:

wherein n is from about 12 to about 75, more preferably, n has anaverage value of about 45.

In one preferred embodiment, the main chain polymer of the graftcopolymer of the invention comprises monomer units which are selectedfrom the group consisting of acrylate esters, methacrylate esters,styrene, acrylic acid, methacrylic acid, and combinations thereof. Morepreferably, the monomer units are methyl methacrylate, allylmethacrylate, or combinations thereof.

The graft copolymer having hydrophobic and/or hydrophilic segments maybe prepared by a process comprising the steps of:

(A) contacting the following components to produce a polymerizable graftcopolymer:

-   (i) a compound represented by:    H—W—Y    wherein W is selected from the group consisting of a hydrophilic    segment and a hydrophobic segment and Y is selected from the group    consisting of a hydrophilic segment and a hydrophobic segment, with    the proviso that when W is a hydrophilic segment, Y is selected from    the group consisting of a hydrophilic segment and a hydrophobic    segment, with the further proviso that when W is hydrophobic, Y is a    hydrophilic segment, and-   (ii) a polymerizable monomer selected from the group consisting of    compounds represented by:

wherein each R¹ is independently selected from the group consisting of:—H, alkyl, aryl, aralkyl, alkaryl, halogen and cyano; R⁴ is selectedfrom the group consisting of: —H, alkyl, halogen, cyano, nitro, alkoxy,alkoxycarbonyl, acyl and a combination thereof; and X is glycidyloxy ora leaving group selected from the group consisting of: halogen, alkoxyand aryloxy, to produce a polymerizable graft monomer; and(B) copolymerizing the polymerizable graft monomer and one or morecomonomers at a temperature and for a period of time sufficient toproduce the graft copolymer. When necessary, the contacting step takesplace in the presence of a catalyst.

Preferably, the comonomer is one or more of the following: styrene,substituted styrene, alpha-methylstyrene, acrylate ester, methacrylateester, acrylonitrile, acrylamide, methacrylamide, vinyl halide, vinylester, vinyl ether and an alpha-olefin.

The preferred polymerizable monomer can be any monomer that is capableof reacting with H—W—Y and include polymerizable monomers, such as,m-isopropenyl-a, a-dimethylbenzyl isocyanate, acryloyl chloride andmethacryloyl chloride. The reaction is typically carried out in thepresence of a catalyst, which is preferably a base, a tin compound or amixture thereof. In a reaction that admits to an acid catalyst, an acidcatalyst such as a Lewis or protic acid may be used.

Preferably, the compounds represented by the formula H—W—Y can be one ormore of compounds represented by:

wherein each of R⁷, R⁸, R⁹ and R¹⁰ is hydrogen; R³ can be —H or alkyl; Ycan be alkyl, acyloxy, alkoxy or carboxylate; and n is from about 12 toabout 250.

The graft copolymer is typically obtained by a free-radicalcopolymerization of the graft monomer and the comonomer, preferably at acomonomer to graft monomer weight ratio of from about 99:1 to about45:55.

Alternatively, the graft copolymer can be prepared by firstcopolymerizing a polymerizable monomer according to the presentinvention with one or more comonomers at a temperature and for a periodof time sufficient to produce a graftable copolymer and thereaftergrafting the group —W—Y onto the graftable copolymer. Such grafting canbe achieved by contacting in the presence of a catalyst the abovegraftable copolymer and a compound represented by:H—W—Ywherein W can be a hydrophilic segment or a hydrophobic segment and Ycan be a hydrophilic segment and a hydrophobic segment, with the provisothat when W is a hydrophilic segment, Y is either a hydrophilic segmentor a hydrophobic segment, with the further proviso that when W ishydrophobic, Y is a hydrophilic segment.

The graft copolymers of the present invention may be prepared byreacting hydroxy-functional or amine functional polyethylene glycolmonoalkyl ethers with polymers having co-reactive groups, including acidchloride, isocyanate and anhydride groups. The side chains may furthercomprise a hydrophobic segment between the PEO segment and the mainchain, and a hydrophobic segment at the terminus of the PEO side chains.Other methods of preparation of the graft copolymers of the presentinvention include the methods described in U.S. Pat. No. 6,582,882,herein incorporated by reference.

The main chain polymer of the graft copolymers may be an additionpolymer or a condensation polymer. Addition polymers are preferablyprepared from acrylate and methacrylate esters, acrylic and methacrylicacid, acrylamides and methacrylamides, acrylonitrile andmethacrylonitrile, styrene, vinyl phenol and combinations thereof Morepreferably, addition polymers are prepared from styrene,methylmethacrylate, allyl acrylate and methacrylate, acrylic andmethacrylic acid, and combinations thereof. Preferably condensationpolymers are polyurethanes, epoxy resins, polyesters, polyamides andphenolic polymers, including phenol/formaldehyde and pyrogallol/acetonepolymers.

The polymeric binder may also comprise a mixture of graft copolymerseach comprising a main chain polymer and polyethylene oxide side chains.The main chain polymer of each graft copolymer is independently selectedfrom an addition polymer or a condensation polymer. Preferable additionpolymers are homopolymers and copolymers of monomers independentlyselected from the group consisting of acrylate and methacrylate esters,including allyl acrylate and methacrylate, acrylic and methacrylic acid,acrylamides and methacrylamides, acrylonitriles and methacrylonitriles,styrene, vinyl phenol and combinations thereof. Preferable condensationpolymers are independently selected from polyurethanes, epoxy resins,polyesters, polyamides or phenolic polymers, includingphenol/formaldehyde and pyrogallol/acetone condensation polymers.

The block copolymers of the present invention can be made byconventional procedures, including anionic, cationic, and free radicalpolymerization. Atom transfer radical polymerization (ATRP) andreversible addition-fragmentation chain transfer (RAFT) polymerizationcan be particularly convenient methods. PEO block copolymers areconveniently prepared by ATRP methods, as described by M. Ranger, etal., “From well-defined diblock copolymers prepared by a versatile atomtransfer radical polymerization method to supramolecular assemblies,”Journal of Polymer Science, Part A: Polymer Chemistry, Vol. 39 (2001),pp. 3861-74.

The at least one non-polyethylene oxide block of the block copolymersmay be an addition polymer or a condensation polymer. The additionpolymers are preferably homopolymers or copolymers of monomers selectedfrom acrylate or methacrylate esters, including allyl acrylate ormethacrylate, acrylic or methacrylic acid, acrylamides ormethacrylamides, acrylonitrile or methacrylonitrile, styrene, or vinylphenol. Preferable condensation polymers are polyurethanes, epoxyresins, polyesters, polyamides and polyureas.

In one preferred embodiment of the invention, the at least onenon-polyethylene oxide block of the block copolymers does not comprisepolyalkylene oxide segments. In another preferred embodiment, the atleast one non-polyethylene oxide block comprises homopolymers orcopolymers of monomers selected from the group consisting of methylmethacrylate, allyl acrylate and methacrylate, acrylic and methacrylicacid, styrene, vinyl phenol and combinations thereof.

The polymeric binder may comprise a mixture of block copolymers eachcomprising at least one PEO block and at least one non-PEO block, asdescribed above. In addition, the polymeric binder may comprise amixture of graft and block copolymers, as described above.

In another embodiment of the invention, the polymerizable compositioncomprises discrete particles. The particles may include a mixture ofcopolymers, which contain various possible combinations of monomericunits. Preferably, the discrete particles are particles of the polymericbinder which are suspended in the polymerizable composition. In aparticularly preferred embodiment, the polymeric binder comprises atleast one graft copolymer. The diameter of the particles in thesuspension may range between about 60 nm and about 300 nm in diameter.The presence of such discrete particles tends to promote developabilityof the unexposed areas.

The substrate of the imageable element is typically an aluminum sheet.However, other materials that are commonly known to those skilled in theart can also be used. Suitable substrates include any sheet materialconventionally used to prepare lithographic printing plates, includingmetals such as aluminum sheets; paper; paper coated on one or both sideswith an alpha-olefin polymer such as polyethylene; films such ascellulose acetate film, polyvinyl acetal film, polystyrene filmpolypropylene film, polyester film such as polyethylene terephthalatefilm, polyamide film, polyamide film, nitrocellulose film, polycarbonatefilm, polyvinyl chloride film; composite films such as polyester,polypropylene or polystyrene film coated with polyethylene film;metallized paper or films; metal/paper laminates and the like.

The surface of plastic films may be treated using the surface treatmenttechniques known in the art to improve adhesion between the substrateand organic coatings.

A preferred substrate is an aluminum sheet. The surface of the aluminumsheet may be treated with metal finishing techniques known in the artincluding physical roughening, electrochemical roughening, chemicalroughening, anodizing, and silicate sealing and the like. If the surfaceis roughened, the average roughness (Ra) is preferably in the range from0.1 to 0.8 μm, and more preferably in the range from about 0.1 to about0.4 μm. The preferred thickness of the aluminum sheet is in the rangefrom about 0.005 inch to about 0.020 inch. The preferred substrate iselectrochemically-grained and anodized aluminum, such as commonly usedfor lithographic printing plates.

Anodic pore size for sulfuric acid anodization is typically less than 20nm whereas anodic pore size for phosphoric acid anodization is typicallygreater than 30 nm. The use of large anodic pore substrates that arephosphoric acid anodized is preferred over sulfuric acid-anodizedsubstrates. Other conventional anodization methods can also be used inthe preparation of the anodized substrate of the present invention,including particularly those that produce an anodic pore size largerthan anodic pore size produced by sulfuric acid anodization.

The polymerizable composition can be applied onto the substrate as asolution or dispersion in the coating liquid of the image-forming layerby a suitable coating method. Illustrative of such a method isdissolving the graft copolymer in an organic water immiscible solvent,dispersing the resulting solution in an aqueous medium, applying theresulting dispersion onto a substrate and thereafter removing thesolvent by evaporation. After proper drying, the coating weight of thelayer is preferably in the range of about 0.2 to about 5.0 g/m², andmore preferably in the range from about 0.7 to about 2.5 g/m².

Preferably, imaging is carried out using an infrared laser and aradiation absorber for absorbing IR radiation. However, UV and visiblelaser imaging may also be used together with an appropriate radiationabsorber. Accordingly, the imageable composition of the presentinvention can further comprise a radiation absorber, which may serve asa sensitizer for promoting polymerization or as a material that iscapable of converting electromagnetic radiation into heat.

The imageable element may further comprise an overlying layer. Onepossible function of the overlying layer is to serve as an oxygenbarrier layer by comprising an oxygen-impermeable compound. The term“oxygen-impermeable compound” is intended to mean a compound thatprevents the diffusion of oxygen from the atmosphere into the layerduring the lifetime of the radicals generated by IR exposure. Theoverlying layer should be soluble, dispersible or at least permeable tothe developer. Other possible functions of an overlying layer include:

-   (1) to prevent damage, such as scratching, of the surface layer    during handling prior to imagewise exposure;-   (2) to prevent damage to the surface of the imagewise exposed areas,    for example, by over-exposure which could result in partial    ablation; and-   (3) to facilitate developability of the unexposed areas.

Preferably, the imagewise exposure step of the method of the inventionis performed with radiation in the range of about 300 to about 1400 nm,preferably about 350 to about 900 nm.

Preferably, development with aqueous developer does not involve aseparate development step. The printing plate may be directly mounted onpress, wherein the non-exposed areas are removed by fountain solutionand/or ink, thereby avoiding a separate development step. It is notedthat plates designed for on-press development can also be developed witha conventional process using a suitable aqueous developer. The platesdisclosed in this invention include on-press developable plates as wellas plates which are intended for other development processes.

The aqueous developer composition is dependent on the nature of thegraft copolymer composition. Common components of aqueous developersinclude surfactants, chelating agents, such as salts of ethylenediaminetetraacetic acid, organic solvents, such as benzyl alcohol, and alkalinecomponents, such as, inorganic metasilicates, organic metasilicates,hydroxides and bicarbonates. The pH of the aqueous developer ispreferably within about 5 to about 14, depending on the nature of thegraft copolymer composition.

Following development, a postbake may optionally be used to increasepress life.

In addition to the thermally imageable layer, the thermally imageableelement can have additional layers, such as an underlying layer.Possible functions of an underlying layer include:

-   (1) to enhance developability of the imagewise unexposed areas; and-   (2) to act as a thermal insulating layer for the imagewise exposed    areas.

Such a thermal insulating polymeric layer prevents otherwise rapid heatdissipation, for example, through the heat conducting aluminumsubstrate. This allows more efficient thermal imaging throughout thethermally imageable layer, particularly in the lower sections. Inaccordance with these functions, the underlying layer should be solubleor at least dispersible in the developer and, preferably, have arelatively low thermal conductivity coefficient.

The invention is further described in the following examples, which areintended to be illustrative and not limiting.

EXAMPLE 1 Synthesis of Macromer 1

Toluene (266 g) was charged into a 500-mL flask, followed by theaddition of poly(ethyleneglycol monomethyl ether) (80 g) (Mn 2000) andmethacryloyl chloride (4.2 g) in a N₂ atmosphere. Subsequently,triethylamine (4.52 g) was added over a period of 20 minutes, whilemaintaining the reaction temperature at 30° C. After an additional 2 hr,the temperature of the reaction mixture was raised to 50° C. and kept atthat temperature for an additional 2 hr. Subsequently, the reactionmixture was cooled to room temperature and filtered to remove thetriethylamine hydrochloride salt, which was obtained in the theoreticalamount. Petroleum ether was added to the filtrate to precipitateMacromer 1, which was collected by filtration and dried in vacuum ovenat room temperature. The reaction is shown in the scheme above.Preferably, the average value of n is about 45.

EXAMPLE 2 Synthesis of Graft Copolymer 1

Macromer 1 (7.5 g), water (48 g) and 1-propanol (192 g) were chargedinto a 500-mL flask, which was heated to 80° C. Styrene (66.9 g) and azobis-isobutyronitrile (0.48 g) (VAZO-64, from DuPont de Nemours Co) weremixed in a separate beaker and part of this solution (12 g) was added tothe macromer solution, which became hazy within about 10 minutes.Subsequently, the remaining solution was added over a 30-min period.After 3 additional hours, the conversion to Graft Copolymer 1 was about97% based on determination of percent non-volatiles. The weight ratio ofstyrene: Macromer 1 was about 90:10 in graft copolymer 1.

EXAMPLE 3 Preparation of On-Press Developable Printing Plate

On a brush-grained and phosphoric acid anodized aluminum substrate thathas been subbed by polyacrylic acid, the solution described in Table 1was applied to give a dry coating weight of 2 g/m².

TABLE 1 Composition of Example 3 (formulations in parts by weight) Partsby Component Weight Percent Reaction product of 3.74 DESMODUR ® N100with hydroxyethyl acrylate and pentaerythritol triacrylate Graftcopolymer 1 3.53 SARTOMER 355¹ 0.78 2-(4-methoxyphenyl)-4,6- 0.42bis(trichloromethyl)-2-triazine Anilino-N,N-diacetic acid 0.23 IR dye²0.09 BYK 307³ 0.02 n-Propanol 72.95 Water 18.24 ¹SARTOMER 355 is amultifunctional acrylic monomer available from SARTOMER Co., Inc. ²TheIR dye is2-[2-[2-phenylthio-3-[(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)ethylidene]-1-cyclohexen-1-yl]ethenyl]-1,3,3-trimethyl-3H-indoliumchloride. ³BYK 307 is a modified polysiloxane available from Byk Chemie.

The resulting coating was then over-coated with a solution of polyvinylalcohol (5.26 parts) and polyvinylimidazole (0.93 parts) in isopropanol(3.94 parts) and water (89.87 parts) to give a dry coating weight of 2g/m². The resulting plate was imaged on a Creo Trendsetter 3244× at 250mJ/cm² and then mounted directly on an AB Dick press. The plate printedmore than 500 copies of good quality prints. A second plate was imagedwith an Olec vacuum frame (5 kW bulb) for 12 units at medium intensity.The plate was mounted on an AB Dick press and more than 500 good qualitycopies resulted.

EXAMPLE 4 Preparation of UV Sensitive On-Press Developable PrintingPlate

Example 3 was repeated except IR dye was removed and no over-coat wasapplied. The resulting plate was imaged with an Olec vacuum frame (5 kWbulb) for 6 units at medium intensity. The plate was mounted, on an ABDick press and more than 300 good quality copies resulted.

EXAMPLE 5 Preparation of Visible Light Sensitive On-Press DevelopablePrinting Plate

On a brush-grained and phosphoric acid anodized aluminum substrate thathas been subbed by polyacrylic acid, the solution described in Table 2was applied to give a dry coating weight of 1.3 g/m².

TABLE 2 Composition of Example 5 (formulation in parts by weight) Partsby Component Weight Percent Reaction product of DESMODUR 2.44 N100 withhydroxyethyl acrylate and pentaerythritol triacrylate Graft copolymer 12.22 SARTOMER 355¹ 0.51 Diphenyliodonium chloride² 0.29Anilino-N,N-diacetic acid 0.23 Ketocoumarin 93⁴ 0.06 BYK 307³ 0.02n-Propanol 75.38 Water 18.85 ¹SARTOMER 355 is a multifunctional acrylicmonomer available from SARTOMER Co., Inc. ²Diphenyliodonium chloridefrom Aldrich. ³BYK 307 is a modified polysiloxane available from BykChemie. ⁴Ketocoumarin 93 has the following structure:

The resulting coating was then over-coated as described in Example 3 togive a dry coating weight of 2 g/m². The resulting plate was imaged onan Oriel 1000 W Solar Simulator model #81291 (Oriel Instruments,Stratford, Conn.) fitted with a 530 nm filter for 5 sec at 4 mW/cm².

The plate was processed in a sink with water and a solution of 30% Varn142W/30% Varn Par, then mounted directly on an AB Dick press. The plateprinted more than 500 copies of good quality prints.

EXAMPLE 6 Synthesis of Graft Copolymer 2

Deionized water (314.8 g) and sodium dodecyl sulfate (2.0 g) werecharged in one-liter 4-neck flask under nitrogen atmosphere and heatedto 70° C. A pre-mixture of ammonium persulfate (0.65 g) and deionizedwater (20 g) were added at 70° C. in 15 minutes. A pre-mixture ofstyrene (79.5 g), Macromer 1 (10 g) and acrylic acid (7.9 g) were addedin 3 hours at 70° C. One and one-half hour later, the % non-volatileswere found to be 22.5% versus 23% (theoretical). The reaction mixturewas cooled to room temperature with water. An ammonium hydroxidesolution (8 g) was added at room temperature to stabilize the latex.

EXAMPLE 7 Preparation of IR Sensitive Printing Plate

Example 3 was repeated except that no over-coat was applied and GraftCopolymer 1 was replaced by Graft Copolymer 2 to illustrate the effectof binder acid number. FIG. 1 shows a scanning electron microscope(‘SEM’) analysis of the resulting coating. As shown in FIG. 1, thecoating comprises discrete particles. The diameter of the particles isup to about 60 nm.

The resulting plate was imaged on a Creo Trendsetter 3244x at 496 mJ/cm²and then mounted on a Komori press. The plate was then treated withPrisco liquid plate cleaner. The plate printed more than 27,500 copiesof good quality prints.

EXAMPLE 8 Synthesis of Graft Copolymer

Macromer 1 (7.5 g), water (48 g) and 1-propanol (192 g) were chargedinto a 500-mL flask, which was heated to 80° C. Allyl methacrylate (66.9g) and VAZO-64 (0.48 g) were added slowly. Within ten minutes of theaddition of this monomer, gelation of the reaction mixture occurred.Therefore, the reaction mixture was discarded and the procedure wasmodified as follows below.

2-Butanone (384.1 g) and Macromer 1 (4.25 g) were charged in one-liter4-neck flask under nitrogen atmosphere and heated to 80° C. Apre-mixture of allyl methacrylate (38.0 g) and VAZO-64 (0.3 g) wereadded at 800 C in 90 minutes. After the addition was complete, anadditional 0.13 gram of VAZO-64 was, added. Thereafter two additionaldoses of VAZO-64 of 0.13 gram each were added. The polymer conversionbased on % non-volatiles was 90%. The weight ratio of allylmethacrylate:Macromer 1 was about 90:10 in Graft Copolymer 3.

The resin solution was precipitated in powder form using hexane (1200 g)and stirred at 3000 RPM using a high shear mixer for 15 to 20 minutes.Then the solution was filtered and the product dried at roomtemperature.

EXAMPLE 9 Preparation of IR Sensitive On-Press Developable PrintingPlate

Example 3 was repeated except that the Graft Copolymer 1 was replaced byGraft Copolymer 3 and no over-coat was applied. FIG. 2 shows an SEManalysis of the resulting coating. As shown in FIG. 2, the coating doesnot comprise discrete particles.

The resulting plate was imaged on a Creo Trendsetter 3244x at 496 mJ/cm²and then mounted directly on an AB Dick press. The plate printed morethan 1000 copies of good quality prints.

Another plate, prepared accordingly, and imaged on the Creo Trendsetterat 361 mJ/cm², was mounted on a Komori press fitted with a hard blanketand using Equinox ink. The plate printed more than 40,000 copies of goodquality prints.

EXAMPLE 10 Preparation of IR Sensitive On-Press Developable PrintingPlate

Example 3 was repeated except that the brush grain substrate wasreplaced by an electrochemically grained substrate with the anodic oxidelayer sealed by polyvinyl phosphonic acid.

The resulting plate was imaged on a Creo Trendsetter 3244x at 250 mJ/cm²and then mounted directly on an AB Dick press. The plate printed morethan 500 copies of good quality prints.

EXAMPLE 11 Synthesis of Graft Copolymer 4

Macromer 1 (20 g of a 50% aqueous solution), obtained from Aldrich andused as received, water (50 g) and 1-propanol (240 g) were charged intoa 1000-mL flask, which was heated to 80° C. Methyl methacrylate (89.4 g)and VAZO-64 (0.65 g) were mixed in a separate beaker and part of thissolution (12 g) was added to the macromer solution, which became hazywithin about 10 minutes. Subsequently, the remaining solution was addedover a 90-min period. After 3 additional hours, the conversion to GraftCopolymer 4 was about 97% based on determination of percentnon-volatiles. The weight ratio of methyl methacrylate:Macromer 1 wasabout 90:10 in Graft Copolymer 4.

In an alternative procedure, a solution of Macromer 1 (7.5 g), dissolvedin a mixture of water (48 g) and 1-propanol (192 g) was charged into a500-mL flask, which was heated to 80° C. Methyl methacrylate (66.9 g)and VAZO-64 (0.48 g) were mixed in a separate beaker and part of thissolution (12 g) was added to the macromer solution, which became hazywithin about 10 minutes. Subsequently, the remaining solution was addedover a 30-min period. After 3 additional hours, the conversion to GraftCopolymer 4 was about 97% based on determination of percentnon-volatiles. The weight ratio of methyl methacrylate:Macromer 1 wasabout 90:10 in Graft Copolymer.

EXAMPLE 12 Preparation of IR Sensitive Printing Plate

Example 3 was repeated except that the Graft Copolymer 1 was replaced byGraft Copolymer 4, prepared from Macromer 1 obtained from Aldrich. FIG.3 shows an SEM analysis of the resulting coating. As shown in FIG. 3,the coating does not comprise discrete particles.

The resulting plate was imaged on a Creo Trendsetter 3244x at 100 mJ/cm²and then mounted directly on an AB Dick press. However, the use of GraftCopolymer 4 by itself did not provide sufficient differentiation fordevelopability of the unexposed areas and durability of the exposedimage areas.

EXAMPLE 13 Synthesis of Graft Copolymer 5

Macromer 1 (7.0 g), deionized water (60 g) and n-propanol (240 g) werecharged in a 1-liter flask and heated to 83° C. In a separate beaker,styrene (92.4 g) and VAZO-64 (0.65 g) were mixed together. Part of thismixture (12 g) was added and 30 minutes later the remaining solution wasadded in two hours. After 3 additional hours, the conversion to GraftCopolymer 5 was about 97% based on determination of percentnon-volatiles. The weight ratio of styrene:Macromer 1 was 93:7.

EXAMPLE 14 Preparation of IR Sensitive On-Press Developable PrintingPlate

Example 3 was repeated except that the graft copolymer 1 was replaced byGraft Copolymer 5 and no over-coat was applied.

The resulting plate was imaged on a Creo Trendsetter 3244x at 250 mJ/cm²and then mounted directly on an AB Dick press. The plate printed morethan 400 copies of good quality prints.

EXAMPLE 15 Synthesis of Macromer 2

Toluene (25 g) was charged into a 500 mL flask, equipped with a DeanStark trap filled with toluene, followed by the addition of polyethylene glycol, monomethyl ether (PEGME) (225 g), Mn 2000, in a N₂atmosphere. The reaction mixture was heated to 1100° C. and held at thistemperature for 2 hr to remove any water by azeotropic distillation.Subsequently, the mixture was cooled to 70° C. and dibutyl tin dilaurate(0.225 g) was added, followed by the addition of m-isopropenyl-a,a-dimethylbenzyl isocyanate (23.6 g) (m-TMI, from Cytec Industries, WestPatterson, N.J.) over a 30 min period at 70° C. After an additional 2 hrat 70° C., the reaction was completed, as evidenced by the disappearanceof the NCO group, as determined by titration and FT-IR analysis.Subsequently, the solution was poured into a glass tray, resulting in awaxy solid material after 1 day. This material was dissolved in methylethyl ketone (300 g), followed by the addition of petroleum ether (2000g), which resulted in the precipitation of solid Macromer 2, which wascollected by filtration and dried in vacuum oven at room temperature.

EXAMPLE 16 Synthesis of Graft Copolymer 6

Macromer 2 (7.5 g), water (48 g) and 1-propanol (192 g) were chargedinto a 500-mL flask, which was heated to 80° C. Styrene (66.9 g) andVAZO-64 (0.48 g) were mixed in a separate beaker and part of thissolution (12 g) was added to the macromer solution, which became hazywithin about 10 minutes. Subsequently, the remaining solution was addedover a 30-min period. After 3 additional hr, the conversion to graftcopolymer 6 was about 97% based on determination of % non-volatiles. Theweight ratio of styrene:Macromer 2 was about 90:10 in Graft Copolymer 6.

EXAMPLE 17 Preparation of IR Sensitive On-Press Developable PrintingPlate

Example 3 was repeated except that the Graft Copolymer 1 was replaced byGraft Copolymer 6.

The resulting plate was imaged on a Creo Trendsetter 3244x at 100 mJ/cm²and then mounted directly on an AB Dick press. The plate printed morethan 500 copies of good quality prints.

EXAMPLE 18 Preparation of IR Sensitive On-Press Developable PrintingPlate Without Over-Coat

Example 3 was repeated except that the over-coat was not applied. FIG. 4shows an SEM analysis of the resulting coating. As shown in FIG. 4, thecoating comprises discrete particles. The diameter of the particles isup to about 100-200 nm.

The resulting plate was imaged on a Creo Trendsetter 3244x at 250 mJ/cm²and then mounted directly on an AB Dick press. The plate printed morethan 600 copies of good quality prints.

EXAMPLE 19 Preparation of On-Press Developable Printing Plate

Example 7 was repeated except that Graft Copolymer 2 was replaced by acombination of graft copolymer 1 (3.35 parts by weight) and GraftCopolymer 2 (0.18 parts by weight). FIG. 5 shows an SEM analysis of theresulting coating. As shown in FIG. 5, the coating comprises discreteparticles. The diameter of the particles is up to about 100-200 nm.

The resulting plate was imaged on a Creo Trendsetter 3244x at 496 mJ/cm²and then mounted on an AB Dick press. The plate printed more than 1,000copies of good quality prints.

Another plate, prepared and imaged accordingly, was mounted on a Komoripress fitted with a hard blanket and using Equinox ink. The plateprinted more than 30,000 copies of good quality prints.

COMPARATIVE EXAMPLE 1 Preparation of IR Sensitive On-Press DevelopablePrinting Plate Without Free-Radical Generator

Example 18 was repeated except that2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-2-triazine in thephotopolymerizable coat was omitted.

The resulting plate was imaged on a Creo Trendsetter 3244x at 250 mJ/cm²and then mounted directly on an AB Dick press. The coating washed offentirely and no prints resulted as there was no image on the plate.

Although the present invention has been described in connection withspecific exemplary embodiments, it should be understood that variouschanges, substitutions and alterations can be made to the disclosedembodiments without departing from the spirit and scope of the inventionas set forth in the appended claims.

1. A method for preparing a printing plate, the method comprisingproviding a substrate; applying a negative-working layer comprising aradiation sensitive composition onto the substrate, wherein theradiation sensitive composition is ink receptive upon exposure toinfrared imaging radiation and comprises an infrared-radiation absorber,a free radical initiator system comprising an electron acceptor and acoinitiator capable of donating electrons, donating hydrogen atoms, orforming a hydrocarbon radical, a polymerizable compound, and betweenabout 10 and about 90 weight percent of a polymeric binder, wherein thepolymeric binder comprises at least one graft copolymer comprising amain chain polymer and polyethylene oxide side chains, or a combinationof said graft copolymer with a block copolymer having at least onepolyethylene oxide block; imagewise exposing the negative-working layerto infrared radiation; and developing the negative-working layer on apress by contacting with ink and/or fountain solution to produce aprinting plate, wherein the method does not comprise a separatedevelopment step.
 2. The method of claim 1, wherein the imagewiseexposing step is carried out using an infrared laser.
 3. A method forpreparing a printing plate, the method comprising providing a substrate;applying a negative-working layer comprising a radiation sensitivecomposition onto the substrate, wherein the radiation sensitivecomposition is ink receptive upon exposure to ultraviolet imagingradiation and comprises an ultraviolet-radiation absorber, a freeradical initiator system comprising an electron acceptor and acoinitiator capable of donating electrons, donating hydrogen atoms, orforming a hydrocarbon radical, a polymerizable compound, and betweenabout 10 and about 90 weight percent of a polymeric binder, wherein thepolymeric binder comprises at least one graft copolymer comprising amain chain polymer and polyethylene oxide side chains, or a combinationof said graft copolymer with a block copolymer having at least onepolyethylene oxide block; imagewise exposing the negative-working layerto ultraviolet radiation; and developing the negative-working layer on apress by contacting with ink and/or fountain solution to produce aprinting plate, wherein the method does not comprise a separatedevelopment step.
 4. A lithographic printing plate precursor comprising:a substrate; and a polymerizable composition coated onto the substrate,the polymerizable composition being ink receptive upon exposure toimaging ultraviolet or infrared radiation and comprising a polymerizablecompound and between about 10 and about 90 weight percent of a polymericbinder; wherein the polymeric binder is a graft copolymer having ahydrophobic backbone and a plurality of pendant groups comprisingpolyethylene oxide segments, the pendent groups being represented by-Q-W—Y wherein: Q is a difunctional connecting group; and the segment—W—Y is represented by —(O—CH₂CH₂)_(n)—OR¹⁶ wherein R¹⁶ is an alkyl of1-5 carbon atoms, and n is from about 12 to about 75, wherein thepolymerizable composition also comprises a free radical initiator systemcomprising an electron acceptor and a coinitiator capable of donatingelectrons, donating hydrogen atoms, or forming a hydrocarbon radical. 5.The lithographic printing plate of claim 4 wherein R¹⁶ is methyl.
 6. Alithographic printing plate precursor comprising: a substrate; and apolymerizable composition coated onto the substrate, the polymerizablecomposition being ink receptive upon exposure to imaging ultraviolet orinfrared radiation and comprising a polymerizable compound and betweenabout 10 and about 90 weight percent of a polymeric binder; wherein thepolymeric binder is a graft copolymer comprising units represented by

wherein n is from about 12 to about 75, and wherein the polymerizablecomposition also comprises a free radical initiator system comprising anelectron acceptor and a coinitiator capable of donating electrons,donating hydrogen atoms, or forming a hydrocarbon radical.
 7. Alithographic printing plate precursor comprising: a substrate; and apolymerizable composition coated onto the substrate, the polymerizablecomposition being ink receptive upon exposure to imaging ultraviolet orinfrared radiation and comprising a polymerizable compound and betweenabout 10 and about 90 weight percent of a polymeric binder; wherein thepolymeric binder is a graft copolymer comprising units represented by

wherein n is from about 12 to about 75, wherein the polymerizablecomposition also comprises a free radical initiator system comprising anelectron acceptor and a coinitiator capable of donating electrons,donating hydrogen atoms, or forming a hydrocarbon radical.